Again, I know this is some coeff of the product of some series, but I dont know how to find the series or the coeff.

I dont know how to go about it.

Is this the whole question?

To evaluate it, wouldn't you actually need to know what the [itex]C_i[/itex] actually are?

Because if they're unknown constants, then I have no idea what is meant by evaluating that. Plus, your equation is not totally clear. You have a negative randomly put it where all the others are positives. You should explicitly write when the negatives are to be.